The Great Lakes Entomologist

Volume 17 Number 2 - Summer 1984 Number 2 - Summer Article 1 1984

June 1984

Identification and Distribution of Nymphs (Ephemeroptera: ) in Wisconsin

William L. Hilsenhoff University of Wisconsin

Follow this and additional works at: https://scholar.valpo.edu/tgle

Part of the Entomology Commons

Recommended Citation Hilsenhoff, William L. 1984. "Identification and Distribution of Baetisca Nymphs (Ephemeroptera: Baetiscidae) in Wisconsin," The Great Lakes Entomologist, vol 17 (2) Available at: https://scholar.valpo.edu/tgle/vol17/iss2/1

This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at [email protected]. Hilsenhoff: Identification and Distribution of Baetisca Nymphs (Epheme

1984 THE GREAT LAKES ENTOMOLOGIST 51

IDENTIFICATION AND DISTRIBUTION OF BAETISCA NYMPHS (EPHEMEROPTERA: BAETISCIDAE) IN WISCONSIN l William L. Hilsenhoff2

ABSTRACT

~ymphs of three species of Baetisca (Ephemeroptera: Baetiscidae) have been collected in Wisconsin. Baetisca laurentina was most abundant. occurring in a wide variety of streams and occasionally in impoundments. Baetisca obesa was uncommon and occulTed only in two large rivers, while B. lacustris was somewhat more common and inhabited medium to streams. Except for a few nymphs of B. lacustris that were collected from Green Bay on Lake Michigan, no Baetisca nymphs were found within 100 km of Lake ~fichigan.

In 1981 Pescador and Berner completed a thorough study of the genus Baetisca in .r-;orth America. They synonymized Baetisca baj/wvi Neave, 1934 with McDunnough, 1932 and provided the first key to nymphs of all species in North America. Only three are known from the Great Lakes region, while seven more occur farther east or in the southeastern United States. Nymphs of species in the Great Lakes region can now be easily identified through characters provided in the key below. Identification of nymphs in 286 collections provides insight into the apparent distribu­ tion of Baetisca in Wisconsin (Fig. 1). All species were most commonly found along margins of streams or impoundments in areas of reduced current and a substrate containing a mixture of sand, silt, and detritus. None of the species were collected from counties within 100 km of Lake Michigan (Fig. 1), probably because streams in this part of Wisconsin lack the silt-sand substrate. An exception was the three nymphs of B. lacustris that were collected from the shore of Chambers Island to the west of Door County in Lake Michigan's Green Bay, and they represent the only truly lentic col­ lections, although a few B. laurentina McDunnough, 1932 and B. obesa (Say, 1843) were collected from impoundments. The most abundant and widely distributed species was B. laurentina, with 1325 nymphs being collected from a variety of small and large streams. Only 55 B. obesa nymphs were found, and all of them came from two very large rivers, the Wisconsin and the St, Croix. The 112 B. lacustris nymphs were collected mostly from medium to large rivers. . ~fost nymphs were collected from October through May, and often there was a large disparity in size among individuals in each collection. Large, mature nymphs were collected from late April through June, suggesting that emergence of all species occurred mostly in May and early June. No nymphs were found in July, and only very small nymphs were present in August. By September many nymphs were large enough to identify and by late October some nymphs of B. lacustris and B. laurentina were 6 mm long (excluding tail filaments). Baetisca obesa nymphs, however, did not reach a length of -1- mrn until late November and early December.

'Research supported by the Research Division of the College of Agricultural and Life Sciences, l'niyersity of Wisconsin-Madison. :nepaiunem of Entomology, University of Wisconsin, Madison. WI 53706.

Published by ValpoScholar, 1984 1 The Great Lakes Entomologist, Vol. 17, No. 2 [1984], Art. 1

52 THE GREAT LAKES ENTOMOLOGIST Vol. 17, No.2

Key to Nymphs of Baetisca in Wisconsin and other Great Lakes States

1. Dorsal spines absent from mesonotal carapace; covered dorsally and ventrally with distinctly separated freckle-like spots ...... lacustris 1'. Dorsal spines present on posterior of mesonotal carapace (small in younger nymphs); pigmentation consists of blotches and irregularly spaced spots of various sizes that often coalesce ...... 2 2(1'). Frontal projection inconspicuous, projecting about 1!3 length of an eye; ventral margin of meso notal carapace with a brown border; venter with numerous irregular-sized dark spots ...... laurentina 2' . Bilobed frontal projection prominent, projecting a distance equal to length of an eye; ventral margin of mesonotal carapace without a dark border; venter mostly devoid of dark spots, but with a large dark spot laterally on first 5 abdominal sterna ...... obesa

LITERATURE CITED

Pescador, M. L. and L. Berner. 1981. The family Baetiscidae (Ephemeroptera). Part II Biosystematics of the genus Baetisca. Trans. Amer. Entomo!. Soc. 107: 163­ 228.

Fig. 1. County collection records of Baetisca in Wisconsin.

https://scholar.valpo.edu/tgle/vol17/iss2/1 2